The present invention relates to method and apparatus for degrading antimisting fuel, and more particularly, to such method and apparatus employing a centrifugal pump.
Interest in the use of engine fuels in gas turbine engine applications, e.g., aircraft engines, as a means to control or reduce crash and postcrash fire fatalities has resulted in development of antimisting fuel. The antimisting fuel typically comprises kerosene containing an additive which alters the fuel to provide long-chain molecule polymers. These long-chain molecule polymers provide the fuel with the ability to resist the tendency to mist and ignite in the event of crash or postcrash tank or fuel line rupture.
However, in order for such antimisting fuel to be properly ignited and burned in the engine combustor, it is necessary to degrade the fuel back to its original kerosene molecule structure. In addition, due to the non-Newtonian and highly viscous characteristic of the antimisting fuel, it is also necessary to degrade the antimisting fuel in order to provide satisfactory heat transfer in the engine heat exchangers generally associated with gas turbine engine applications. It is also desirable to degrade the antimisting fuel to ensure predictable leakage in fuel metering components and to avoid blockage of fuel filters.
Centrifugal pumps are well known in gas turbine engine technology. For example, an exemplary centrifugal pump is described in U.S. Pat. No. 3,784,318, entitled "Variable Diffuser Centrifugal Pump," assigned to the assignee of the present application, and hereby incorporated into reference in the present application. Such centrifugal pumps typically have a rotary impeller closely surrounded by a collector, e.g., a vaned diffuser, with the impeller having an input for receiving fuel and an output for directing the fuel therefrom into an input of the surrounding collector. Such centrifugal pumps are capable of pumping fuel at the pressure and flow levels, e.g., typically about 1000 psi (pounds per square inch) and 16,000 pph (pounds per hour), respectively, required for many gas turbine engine applications. In addition, such pumps must operate at required speed ranges in the order of about 25,000 rpm.
In order to employ such a centrifugal pump with antimisting fuel, however, additional means must be provided for degrading the antimisting fuel as conventional centrifugal pumps provide either no degrading capability or unacceptably insufficient degrading capability. Thus, it has been proposed to add degrading structures e.g., throttling devices or cavitating devices, in serial flow relation with the centrifugal pump, thereby providing the required degrading function. However, such additional degrading structures are undesirable due to the additional fuel system complexity and additional failure potentials introduced therewith. In addition, such additional degrading structures typically require a significant increase in engine power extracted and often cause the fuel temperature to rise unacceptably, e.g., to levels over 300.degree. F. at the fuel nozzles.
Thus, it would therefore be desirable to provide a conventional centrifugal fuel pump having the capability to degrade antimisting fuel. More particularly, it would be desirable to provide such a pump having the capability to pump fuel at the pressure and flow levels required in gas turbine engine applications, such as aircraft applications, as well as the capability to simultaneously degrade antimisting fuel.
Accordingly, it is a general object of the present invention to provide improved method and apparatus for degrading antimisting fuel.
It is another object of the present invention to provide such method and apparatus which includes an improved centrifugal pump.
It is another object of the present invention to provide such a centrifugal pump which operates as a relatively high flow range centrifugal pump while degrading antimisting fuel.
It is another object of the present invention to provide such a centrifugal pump having recirculation means for enhancing the degradation of antimisting fuel.
It is another object of the present invention to provide such a centrifugal pump which can be provided through simple modification to a conventional centrifugal pump.